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"Metastasis is the spread of cancer from its primary site to other places in the body" Cancer cells can break away from a primary tumor, penetrate into lymphatic and blood vessels, circulate through the bloodstream, and grow in a distant focus (metastasize) in normal tissues elsewhere in the body. - Wikipedia.org
The term metastasis can evoke fear in patients, likely because it's associated with very poor clinical prognosis in many so-called solid cancers. E.g., breast, colon, lung cancer, etc.
Metastasis of a lymphoma seems a misnomer - that is, an interpretation known not to be true. The normal behavior of lymphocytes (the cell of origin of lymphomas) is to travel or migrate in the blood and lymphatic tissue in order to fight infection. ...
Click the image to enlarge picture showing migration of lymphocytes.
Therefore, "migration" or "extranodal" seem better terms for the spread of a lymphoma than "metastasis," because the change in location does not necessarily mean a profound "change in the behavior of the cancerous cells," that is, from slow growing to rapidly multiplying, or to treatment-resistant disease.
Note: it's common for lymphomas to show up (present) in the blood, bone marrow, and lymphatic organs. The bone marrow is a nursery for blood cells. Thus, the existence of lymphoma cells in the marrow is generally expected, but often reversible.
Some types of lymphoma first present in the skin (Cutaneous), the stomach (Gastric), the lung (Pulmonary), bone (Osteo), eye (Orbital) and other regions. Gastric MALT, a marginal zone lymphoma, tends to stay localized in the gastric mucosal tissue, but it can spread to other areas. That said, scientists and radiologists may use the term metastasis or metastatic behavior when describing changes in the location of lymphomas (as shown in the abstracts below).
The important question seems to be: does the metastatic behavior of a lymphoma have the same clinical connotation as for solid cancers? Fortunately, the answer is often that the spread to a new location does not necessarily predict sensitivity of the lymphoma cells to treatment or the potential for a favorable long-term outcome.
~ KarlS (layperson perspective)
"Lymphoma cells are derived from normal lymphocytes and therefore their metastatic behavior is probably based on mechanisms of migration of these normal progenitors [cells of origin].
Several adhesion molecules that are involved in this normal migration, have been identified. These include the 'lymph node homing receptors' and the leukocyte (beta 2) integrins. The limited evidence available for a role of these molecules in lymphoma metastasis is reviewed here. Recently, the regulation of the activity of adhesion molecules was shown to be of pivotal importance for the control of leukocyte traffic. The implications of these findings for lymphoma metastasis are discussed."
Adhesion molecules in lymphoma metastasis.
Semin Cancer Biol. 1993 Oct;4(5):285-92. Review. PMID: 8257779
The site of origin of lymphoid tissue is an important determinant of lymphocyte migration patterns. The association of gastrointestinal (GI) and Waldeyer's ring lymphoma and the unique lymphocyte migration pattern of gut-associated lymphoid tissue (GALT) have been previously described.
To establish whether predictive clinical patterns of disease occur in localized Non-Hodgkin's lymphoma, survival and relapse patterns for 496 patients with stage I and II non-Hodgkin's lymphoma (NHL) treated with loco-regional irradiation (XRT) alone were examined.
We identified 139 patients with GALT lymphoma (defined as arising from primitive gut and including Waldeyers' ring, thyroid, and GI lymphomas) and 87 patients with extranodal non-gut-associated lymphoma (ENL).
Survival and relapse data were assessed in multifactorial analysis to correct for previously identified other prognostic variables.
GALT lymphomas (GALT-L) have a survival advantage compared with other ENL (P = .017) independent of stage and histology. A difference in distant relapse (DR) rate between GALT-L and other ENL (P = .0002) was also identified. The presentation site of localized extranodal NHL is predictive of clinical behavior and is an independent determinant of outcome. This may be an expression of lymphocytic origin and determinants of migration patterns "
Patterns of disease in localized extranodal lymphomas.
J Clin Oncol. 1987 Jun;5(6):875-80. PMID: 3585443